The present invention relates generally to a piezoelectric actuated fuel injector for use in conjunction with an internal combustion engine and, more particularly, to a method for controlling rail fuel pressure through the use of a piezoelectric actuated fuel injector.
It is well known in the automotive engine art to provide solenoid actuated fuel injectors for controlling the injection of pressurized fuel into the cylinders of an internal combustion engine. Each fuel injector may include an injector body having an axially extending fuel passage therein, a control chamber disposed in the injector body, and an injector valve for controlling fuel flow from the injector. A solenoid actuated control valve may be used to control the fuel pressure in the control chamber, such that the injector valve is axially movable within the fuel passage in accordance with the fuel pressure in the control chamber.
Controlling fuel pressure in the common rail interconnecting the fuel injectors is a critical aspect of achieving accurate fuel injection. In one instance, the fuel injector may be used to relieve fuel pressure to a low pressure fuel return circuit. U.S. Pat. No. 5,711,274 discloses a known method for reducing fuel pressure, where a solenoid actuated control valve is quickly pulsed on/off in order to relieve fuel pressure without axially moving the injector valve within the injector body.
Piezoelectric devices are attractive candidates as control valve actuators in high pressure fuel injection systems. The precise longitudinal deflection characteristic of piezoelectric devices in conjunction with their rapid dynamic response provides the potential of achieving meaningful control over the rate of fuel injection. Additionally, the relative high load capability of piezoelectric devices is consistent with the extremely high pressure environment of common rail fuel injectors.
Therefore, it is desirable to provide a method for controlling fuel pressure in the common rail through the use of a piezoelectric actuated fuel injector. Since the movement of the control valve is proportional to the longitudinal growth of the piezoelectric device, the piezoelectric actuated fuel injector provides better control of the fuel pressure relieved through the low pressure return circuit. It is further desired to the use of the piezoelectric actuated fuel injector to compensate for pressure pulsations within the common rail of the fuel injection system.
In accordance with the present invention, a fuel injection system is provided for controlling fuel pressure in a common rail through the use of a piezoelectric actuated fuel injector. The fuel injection system includes at least one fuel injector having an axially extending fuel passage therein, a control chamber disposed in the injector, an injector valve axially movable within the fuel passage in accordance with a fuel pressure in the control chamber, a control valve for controlling fuel pressure in the control chamber, and a piezoelectric actuator for actuating the control valve. The fuel injection system further includes a pressure sensor for determining a rail pressure in the common rail, and a controller electrically connected to the pressure sensor and to the piezoelectric actuator of at least one fuel injector. In response to a signal from the pressure sensor, the controller actuates the control valve such that the control chamber relieves pressure through a low pressure fuel return circuit without axially moving the injector valve within the injector body, thereby controlling fuel pressure in the system.
For a more complete understanding of the invention, its objects and advantages, refer to the following specification and to the accompanying drawings.